Semiconductor light sources, such as lasers and photodetectors have many applications in modern technology including telecommunications. For many, if not most, applications, it is desirable to have a structure which combines the optical functions performed by the laser or photodetector with the electronic functions performed by, for example, field-effect transistors (FET). In other words, it would be desirable to have a structure that performs the optical and electronic functions on a single substrate. This type of structure yields what is generally referred to as monolithic optoelectronic integration. Such a device structure has a number of possible advantages associated with lower cost: simplier, more rapid processing; better electrical connection; avoidance in dealing with a plurality of semiconductor chips; etc.
There have been attempts to fabricate monolithic integrated optoelectronic circuits combining, for example, a laser with a field-effect transistor. See, for example, Applied Physics Letters 41, p. 126, 1982. Additionally, a laser, field-effect transistor and photodiode have been fabricated to form an optical repeater. Furthermore, lasers have been integrated with electronic circuits containing several FETs to form differential amplifiers. See, for example, IEEE Journal of Lightwave Technology, LT-1, p. 261, 1983.
None of the approaches used in implementing these circuits has yielded completely satisfactory results. The length of the semiconductor laser active area, i.e., the cavity, is generally approximately 300 .mu.m or less. If the skilled artisan wishes to provide cleaved laser facets, the chip must be cleaved to form both ends of the cavity thereby limiting the area available for the electronic devices to a length less than approximately 300 .mu.m although the width may be large.
Several approaches have been taken in attempting to avoid the relatively stringent space limitation imposed by this technique. One approach uses chemical etching, either wet or dry, to fabricate etched mirrors for the laser. This permits a large area to be available for the electronic devices. However, at the present time, etched mirror lasers do not achieve performances which are as good as lasers having cleaved facets.
Another approach involves what is termed microcleaving in an attempt to obtain better quality laser mirrors. A portion of the active layer is undercut to form a free standing member. Ultrasonic vibration is then used to produce a cleave in the member. However, this technique suffers the drawback of having the laser cavity lengths randomly determined, within a range, by the vibration. It suffers the additional practical drawback of not having obtained high yields of good quality facets.